Since epoxy resins have a number of excellent properties, for example, adhesiveness to various substrates, heat resistance, chemical resistance, an electrical property, a mechanical property, etc. as compared with other resins, they are utilized widely in the industrial fields including coating materials aiming at corrosion or beautiful decorativeness, adhesives for civil engineering and construction and the like. In general, though epoxy resin compositions which are used in the fields of coating materials and adhesives are good with respect to a gas barrier property as compared with urethane resins, acrylic resins, polyolefin based resins and the like, they are still inferior to polyvinylidene chloride, polyvinyl alcohol or the like which is classified into a gas barrier material. Accordingly, in the case of utilizing an epoxy resin, for the purpose of enhancing its gas barrier performance, there have been made various contrivances, for example, an increase in thickness of a coating film, covering upon being superimposed with other material, joint use with a filler, etc.
Under such circumstances, with respect to a composition for coating material using an epoxy resin, there is proposed a method for enhancing a gas barrier property against oxygen, carbon dioxide, etc. by increasing an amine nitrogen content in the composition (see Patent Documents 1 and 2). However, in view of the facts that the gas barrier property of such a composition for coating material is not remarkably high and that the barrier property under a high humidity condition is not high, more improvements are desired.
Also, there is proposed a method for more improving the battier property than those in the foregoing compositions and enhancing the barrier property under a high humidity condition by using a composition for coating material, wherein a ratio of active amine hydrogen in a polyamine to an epoxy group in a polyepoxide is at least 1.5/1; and the polyamine is a modified product of a polyamine which is an initial polyamine and in which at least 50% of carbon atoms thereof are aromatic (see Patent Document 3). However, in the foregoing composition for coating material, a large amount of an amine group having unreacted active amine hydrogen remains in the reaction product after coating; and therefore, there are involved such problems that in the case of taking into consideration coating on a metal, a concrete, etc. for the purposes of achieving rustproof and anticorrosion, excellent performances which an epoxy resin originally possesses, for example, adhesiveness, heat resistance, chemical resistance, an electrical property, etc. are not revealed; and that in the case of taking into consideration an adhesive of packaging films for the purpose of achieving gas barrier, adhesiveness and chemical resistance are poor, and performances necessary for use as the adhesive are not revealed.
As methods for solving these problems, there is proposed an epoxy resin composition composed of an epoxy resin and an amine based curing agent (see Patent Document 4).
However, though the foregoing epoxy resin composition reveals good performances in a gas barrier property, adhesiveness and chemical resistance, the curing agent to be used is one obtained by modifying a polyamine, and because of its high reactivity with the epoxy resin, the epoxy resin composition involves such drawbacks that its pot life is short and that its workability is poor.
Meanwhile, in recent years, a packaging material is being watched as an application of epoxy resin compositions. As the packaging material, complex flexible films composed of a combination of polymer materials of a different kind from each other are the mainstream for reasons of their strength, a protection property of goods, working adaptability, an effect of advertising by printing, etc. and the like. In general, such complex films are composed of a thermoplastic plastic film layer which will be an external layer playing a role for protecting goods, etc. and a thermoplastic plastic film layer which will be a sealant layer, etc. In sticking them to each other, there are adopted a dry laminating method wherein an adhesive is coated on a laminated film layer, thereby allowing it to adhere to the sealant layer; and an extrusion laminating method wherein an anchor coating agent is coated on a laminated film layer as the need arises, and a plastic film which will be a molten sealant layer is press bonded and laminated in a film form. Also, as adhesives to be used in these methods, in general, two-pack type polyurethane based adhesives composed of a main agent having an active hydrogen group such as a hydroxyl group, etc. and a curing agent having an isocyanate group are the mainstream from the standpoint of a high adhesive performance (for example, Patent Documents 5 and 6, etc.)
However, in view of the fact that in these two-pack type polyurethane based adhesives, their curing reaction is generally not so fast, in order to secure sufficient adhesiveness, it was necessary to perform curing promotion by means of aging over a long period of time of from one day to 5 days after sticking. Also, in view of the fact that a curing agent having an isocyanate group is used, in the case where the unreacted isocyanate group remains after curing, this residual isocyanate group reacts with moisture in the air to produce carbon dioxide, and therefore, there were involved problems such as generation of bubbles within the laminated film, etc.
As methods for solving these problems, there are proposed a polyurethane based adhesive and an epoxy based adhesive for laminate (for example, Patent Documents 7 and 8).
However, such a polyurethane based adhesive or epoxy based adhesive is not so high in a gas barrier property, and in the case where a packaging material is required to have a gas barrier property, the packaging material was required to be individually laminated with a gas barrier layer of every kind such as a PVDC-coated layer, a polyvinyl alcohol (PVA)-coated layer, an ethylene-vinyl alcohol copolymer (EVOH) film layer, an m-xylyleneadipamide film layer, an inorganic vapor deposited film layer having alumina (Al2O3), silica (Si), etc. vapor deposited thereon, etc. Lamination of such a gas barrier layer of every kind on the packaging material was disadvantageous from the standpoints of manufacturing costs of laminated films and working steps in lamination.    [Patent Document 1] JP-B-7-91367    [Patent Document 2] JP-B-7-91368    [Patent Document 3] JP-T-9-511537    [Patent Document 4] JP-A-2002-256208    [Patent Document 5] JP-A-5-51574    [Patent Document 6] JP-A-9-316422    [Patent Document 7] JP-A-2000-154365    [Patent Document 8] WO 99/60068